Analytical potentiometric and spectroscopic study of the equilibria in the aqueous nickel(II)–triethylenetetramine and nickel(II)–D-penicillamine systems
The complexation of nickel(II) with triethylenetetramine and D-penicillamine has been examined in 0.15 M NaCl solution at 25 °C by a combined potentiometric–spectroscopic approach. Trien (A) forms the following complexes with Ni(II): MA, MA2, MH2A2, M2A3, M2HA3, and M2H2A3 with overall log stability constants: 14.34, 20.64, 37.28, 40.05, 49.20, and 55.02, respectively. Their concentrations as a function of pH are presented and their likely structures discussed. In contrast, D-penicillamine forms the species MA and MA2 only. The latter species, which is the only species from pH 5.8 to 10.0, is shown to be square-planar via coordination of the N, S atoms of the ligand molecules. The overall log stability constants of MA and MA2 are 11.22 and 22.71, respectively. The significance of these results in relation to the effectiveness of these ligands in preventing nickel toxicity in rats is discussed.